The United pref. interview process to my understanding goes like this:
1) After putting in your time at Silver, you will get a pref interview at a United Express Jet operator i.e ExpressJet, GoJet.
2)Once completing your time their, and have obtained PIC time you will then be allowed to interview with United mainline and be based at Guam on airport ready RSV for 8hrs a day.
*just speculating*